1. Field of Invention
The present invention relates to a manufacturing method of a reflective multi-layered thin film mirror for extreme ultraviolet radiation exposure process using atomic force microscope lithography, by forming a metal oxide structure with fixed height and width on a substrate using the anodic oxidation phenomenon between the probe of an atomic force microscope and an absorber for patterning of an absorber material deposited on the multi-layered thin film substrate, wherein the metal oxidic layer is etched to obtain an ultra-fine line patterned absorber.
2. Description of Related Art
In manufacturing semiconductor elements, the optical lithographic process is the core process in creating circuit patterns by refractive light on a substrate coated with a light sensing film sensitive to light. Lasers are used as light sources, but traditional optical exposure processes have reached their limits in that they cannot be applied to manufacturing substrates with a minimum line width of less than 70 nm.
Therefore, new sources of radiation such as extreme ultraviolet radiation (EUV), electron beam, X-ray, and ion beam are being studied, with the extreme ultraviolet radiation and the electron beam being spotlighted as the next generation exposure technologies.
Particularly, the EUV exposure is the most promising technology among many next generation exposure processes, and the reflective multi-layered thin film mirror that allows Bragg reflections may be considered as the core factor in an exposure process using EUV.
A reflective mirror is used to transfer mask images to a semiconductor substrate by reflecting light in EUV exposure process, unlike traditional refractive optical systems and transparent masks. The yield of elements is affected mostly by the reflectivity of each mirror so that manufacture of mirrors with high reflectivity and low imperfection is essential for it to be applied to next generation exposure technology.
Radiations within the range of EUV wavelength are absorbed by matters and cannot pass through them. Thus, laminated structures of Mo layers and Si layers are being used in current development of multi-layered thin film mirrors because of their large differences in optical refraction as described in U.S. Pat. No. 6,110,607.
Further, various other materials have been used to manufacture multi-layered thin films with reflectivity superior than Mo/Si multilayered thin films. For instance, Mo2C/Be multi-layered thin film is described in U.S. Pat. No. 6,229,652, and MoRu/Be multi-layered thin film is described in U.S. Pat. No. 6,228,512.
On the other hand, recent semiconductor technologies demand a decreased element pattern sizes because of high integration of elements with simultaneous integration of many elements, requiring the embodiment of minute patterns during exposure processes in order to decrease pattern sizes of elements.
The next generation lithographic EUV exposure mask requires multi-layered thin films with sufficient reflective property to accommodate the absorption of EUV at 13.5 nm wavelength by matter. And, it is extremely important to obtain minute patterns on absorbers in order to decrease the corresponding pattern sizes of elements.
This type of exposure masks for the next generation lithography also rely on an electron beam lithography apparatus for the implementation of minute patterns like the traditional photo mask as explained below.
As shown in FIG. 1, the manufacturing process of a reflective multi-layered thin film mirror involves deposition of a multi-layered thin film, a capping layer and an absorber layer on a silicon substrate (1), followed by a patterning process. Traditionally, electron beam lithographic technology was used for patterning of an absorber layer.
More specifically, a reflective multi-layered thin film is obtained by depositing a multi-layered thin film (3) such as Mo/Si basic structure, Ru/Mo/Si which is an enhancement of multi-layered thin film material based on basic Mo/Si structure, Mo2C/Be structure, or MoRu/Be structure on silicon substrate (1), then a capping layer (5) such as silicon oxide is deposited on top to protect this multi-layered thin film (3).
Next, an absorber layer (7) such as chromium (Cr) is deposited on above-mentioned multi-layered thin film structure, followed by patterning of an absorber layer (7) such as chromium that has been deposited in the surface of multi-layered thin film structure by electron beam lithography. Chromium (Cr), Tantalum (Ta), or Tungsten (W) is deposited as an absorber material on the multi-layered thin film substrate and coated with resistant material for patterning of this absorber layer.
A resistant layer is patterned into few nm wide grooves by electron beam lithography, substructure of the absorbing thin film processed using dry etching or wet etching, then the resistant materials eliminated by washing to obtain a patterned mask with desired appearance. But, if an electron beam lithography such as the one mentioned above is used to pattern an absorbing layer, electron beam scattering causes damages to the substrate. Minute patterns are also hard to achieve and the attainable line width is limited to around 30 nm.
Therefore, a new method is needed that can maintain the properties of the next generation lithographic EUV exposure mask mirror, overcome the limitations of line with of patterns, and eliminate the need for expensive electron lithography system and high vacuum.
M. Sundermann reported the following results in a published study using gold (Au) as the absorbing material on a Mo/Si multi-layered thin film (M. Sundermann, and 7 others, Surface Science, v. 454-456, p. 1104, 2000). In this study, gold was deposited as the absorber material on the surface of multi-layered thin film, followed by self-assembled monolayer (SAM) as the resistant material on top of it. Then the SAM was selectively corrupted using scanning tunneling microscope lithographic process, and the exposed absorbent material was etched while wetting to obtain a pattern.
But, this method can only be applied to absorbing materials that do not oxidize such as gold. Thus, a method is needed that can be applied to all materials with high absorbance coefficients and allow realization of pattern images with better structural shapes by either wet or dry etching of formed oxidized materials.
The purpose of this invention is to resolve the above-mentioned problems by providing methods to produce reflective multi-layered thin film mirrors for extreme ultraviolet radiation exposure processes that allow realization of few nm wide absorber patterns by using an atomic force microscope, thereby overcoming the line width limitations encountered with the traditional electron beam lithography. This allows monumental decreases in the absorber pattern size of thin film mirrors and does not require an expensive electron beam lithographic device and high vacuum.